1. Field of the Invention
The present invention relates to a light-guide module, more particularly to a light-guide module including a light-guide strip.
2. Description of the Related Art
U.S. Pat. Nos. 5,499,112 and 6,783,254 disclose light-guide strips applicable to scanner and facsimile devices. The light-guide strips serve to guide light passing therethrough onto a target surface to thereby illuminate the target surface with uniform illumination distribution. Shown in FIG. 1 is a light-guide strip 1 disposed such that an illuminating surface thereof is parallel to and faces toward a target surface 2, thereby directing light passing through the light-guide strip 1 and exiting via the illuminating surface onto the target surface 2. Shown in FIG. 2 is a plot of illumination distribution along the target surface 2. It is apparent that such a configuration of the light-guide strip 1 with respect to the target surface 2 may achieve uniform illumination of the target surface 2, whereby visible features (e.g., text and images) on the target surface 2 may be adequately illuminated for image acquisition or optical character recognition processes. The configuration, in which the light-guide strip 1 is disposed such that the illuminating surface thereof illuminates the target surface 2 from a predetermined angle with uniform illumination, may be referred to as “uniform illumination at a specific angle”.
FIG. 3 illustrates a configuration in which first and second image-acquisition modules 3, 4 are disposed at specific positions with respect to the light-guide strip 1 such that light exiting via the illuminating surface of the light-guide strip 1 is directed toward the first and second image-acquisition modules 3, 4. However, referring to FIG. 4, which is a plot of relative brightness distribution along the illuminating surface of the light-guide strip 1, it is apparent that, in such a configuration, images captured by the image-acquisition modules 3, 4 have a non-uniform relative brightness distribution. This is because each of the first and second image-acquisition modules 3, 4 forms an angle with the light-guide strip 1 that varies along the illuminating surface, and each of the first and second image-acquisition modules 3, 4 is spaced apart from the light-guide strip 1 by a distance that varies along the illuminating surface. In addition, light exiting via the illuminating surface is not scattered and hence has high directivity. Therefore, images captured by the first and second image-acquisition modules 3, 4 in such a configuration will have a non-uniform relative brightness distribution. Accordingly, the light-guide strip 1 is not suitable for optical touch-control systems.